This proposal responds to the Request for Cooperative Agreement Applications entitled "Data Coordinating Center for Cooperative Clinical Comparison of Chorion Villus Sampling and Amniocentesis." The cooperative agreement will include representatives from NICHD, several clinical centers, and a data coordinating center. The proposed study will compare two procedures for prenatal diagnosis of abnormalities in the fetus: chorion villus sampling and amniocentesis. The objectives of the study will be to compare the two procedures with respect to accuracy of diagnosis and rates of complications, including bleeding, sepsis, fetal loss, and injury to the fetus. Women seeking genetic counseling prior to the eleventh week of gestation will be asked to participate in a randomized study of the two procedures. Those giving written informed consent will be randomly assigned to one of the two procedures. Those not willing to be randomized will be asked for permission for information about their pregnancy outcomes to be used in the study. The Biostatistics Center of the Department of Statistics and Computer Science, The George Washington University, proposes to serve as the Data Coordinating Center (DCC) for the study. The DCC will participate in all phases of the study, and will be particularly responsible for biostatistical collaboration including design of study forms, data management and computer processing, interim reporting, and statistical analyses. The proposed staff have extensive experience in the design and coordination of cooperative studies, data management and computerization, statistical analysis of data relating to outcomes of pregnancy, and a continuing interest in cooperative research.